The present invention relates generally to a method of making germanium nanocrystals and nanowires, and, more particularly, to a method of making germanium nanocrystals and nanowires from germanium (II) precursors.
Nanometer-sized crystalline semiconductor materials have potential applications in optoelectronics, photovoltaics, and biological imaging. These applications are based on the size-dependent quantum confinement effect, which is found in these nanostructure materials. Hence, the ability to control the size of these nanometer-size materials is import in the control of the material electronic and optical properties.
Large-scale solution synthesis routes for compound semiconductor nanocrystals (NCs) such as CdSe, CdS, CdTe, PbSe, ZnO, InP, and AgBr are available. However, suitable solution synthesis routes for Group IV NCs, such as Si and Ge, are not readily available even though Si and Ge are two important semiconductor materials and have been widely used in microelectronics, power generation and display industries.
The discovery of luminescence in porous Si demonstrated the quantum confinement effect in Si and prompted the development of various synthetic routes to Si NCs. Additionally, Si NCs, embedded in a layer of SiO2, were demonstrated to produce stimulated emission and light amplifications upon excitation with a 390 nm laser source. The measured net material gain is comparable to III-V quantum dots. In comparison to Si NCs, Ge NCs have a larger exciton Bohr radius, which translates to a strong quantum confinement effect even at a relatively large NC radius. Even though bulk Ge is an indirect bandgap material, Ge NCs can behave similarly to a direct bandgap material, which can potentially allow the use of Ge NCs as light-emitting or power-generating elements. Simple and convenient synthetic routes, such as solution synthesis, to the production of Ge NCs are therefore desirable.
Ge NCs have been synthesized by several methods, all of which rely on direct reduction of Ge(IV) precursors to Ge(0). Some methods utilize Na/K as a reducing agent, others use a reaction between Mg2Ge and GeCl4, reduction of GeCl4 or GeI4 using LiAlH4 as a reducing agent, high-pressure reduction, and supercritical fluid methods at high temperature and pressure. These methods encompass the use of reducing agents or salt byproducts in the reaction that makes the separation and purification processes, as well as control over the Ge NC surface, difficult.
Useful would be a solution synthesis process that allows reduction of a Ge precursor to elemental Ge nanocrystals or nanowires from a single precursor without the need for the presence of reducing agents.